Natural cheese varieties (hard and semi-soft) are produced from milk with the addition of a fermented starter culture and a suitable coagulant (rennet) so as to develop the proper flavor, aroma, and desired acidity. The resulting fermented coagulum is then cut and the curd is cooked in its whey. After cooking the whey is drained from the curd and the curd can then be cheddared or stirred while additional acid is produced by fermentation of the lactose to lactic acid in the curd. If cheddared, the curd is then milled, salted and pressed into blocks or hoops for maturing.
The processing conditions are controlled to yield a product in which the residual lactose and unused buffer capacity of the curd are balanced, so that complete fermentation of the residual lactose in the curd to lactic acid will result in a cheese with the proper pH, normally about 4.9 to 5.6.
In order to increase the yield, it has been proposed to alter the composition of whole or skim milk by utilizing ultrafiltration or reverse osmosis ("Composition Of Hard Cheese Manufactured By Ultrafilatration", B. J. Sutherland and G. W. Jameson, Australian Journal of Dairy Technology, pp. 136-143, December 1981). In a process of this type, milk is concentrated by ultrafiltration and diafiltration to about one-fifth of its original volume and the resulting concentrate is then transferred to conventional processing to form cheese either by a batch or continuous process.
In the production of hard type cheese such as cheddar, colby or stirred curd, the curd must be formed, cut, and handled under conditions that allow sufficient whey separation to reduce the moisture to levels acceptable for these cheese varieties. Since the milk has been concentrated by ultrafilatration and diafiltration, less whey is separated than in traditional cheese making. During or following whey separation, the curd must be moved or held for an extended incubation period to allow fermentation of sufficient lactose to achieve the desired final pH in the product. It is this incubation period that has created problems for the continuous manufacture of hard cheese without building large curd incubation systems into the processing equipment.
More recently, a process has been developed in which the moisture content and pH of the final product can be controlled to any desired level. In this process, as described in "Cheese Base For Processing: A High Yield Product From Whole Milk by Ultrafiltration", C. A. Ernstrom, B. J. Sutherland and G. W. Jameson, Journal of Dairy Science, 63, 228, (1980), whole milk is concentrated by ultrafiltration to about 40% of its original milk weight and then diafiltered at constant volume until a desired ratio of lactose to buffer capacity is established and then concentrated by ultrafiltration to about 20% of the starting milk weight. The retentate thus produced is inocculated with a bacteria starter culture and with or without a coagulant and fermented by conventional procedures to completely ferment the residual lactose and obtain precise control of the final pH.